Pt-Frame@Ni <i>quasi</i> Core–Shell Concave Octahedral PtNi₃ Bimetallic Nanocrystals for Electrocatalytic Methanol Oxidation and Hydrogen Evolution

PtNi₃ bimetallic concave octahedrons with a majority of platinum atoms deposited on the frames were synthesized in ethylene glycol solution. The high angle annular dark field scanning transmission electron microscopy (HAAD-STEM) characterizations and energy-dispersive X-ray spectroscopy (EDS) analysis reveal that the Pt frames have a thickness of less than 2 nm, which surround a nickel core thus forming a <i>quasi</i> core–shell concave octahedral nanoparticle (NP). The element-specific anisotropic growth followed by the nanoscale phase segregation and subsequent oxidation of Ni riched facets are responsible for the formation of the concave nanostructure. The PtNi₃ <i>quasi</i> core–shell concave octahedrons exhibit substantially enhanced electrocatalytic properties toward methanol oxidation and hydrogen evolution reaction compared with that of the commercial Pt/C, suggesting that the Ni riched Pt–Ni NPs can be used as a potential candidate for methanol oxidation reaction (MOR) or hydrogen evolution reaction (HER) catalysts with the low utilization of Pt

Strain and Ligand Effects on CO₂ Reduction Reactions over Cu–Metal Heterostructure Catalysts

The strain and ligand effects on the adsorption energies of key intermediates (*COOH, *CO, *CHO, and *COH) in CO₂ reduction reactions on the Cu–M(111) (M = Ni, Co, Cu, Rh, Ir, Pd, Pt) heterolayered catalysts have been quantitatively separated using first-principles calculations. Contrary to the common belief that strain is always the leading factor influencing catalytic performance of the core–shell type heterostructure catalysts, the ligand effect due to the underlying hetero elements should not be ignored and may become dominant for strain-insensitive adsorbates (*CO and *COH). Moreover, the models of Cu­(2 ML/3 ML)–M­(111) (M = Ir, Rh, Pt, Pd) have been shown to be better catalysts for CO₂ reduction, as they require lower overpotential to drive the reaction than the Cu(111) slab. Particularly, the overpotential is predicted to be lowered by 0.17 V for Cu­(3 ML)–Ir(111) model catalyst. Thus, both effects should be considered in heterostructure catalyst design

A Universal Rule for Organic Ligand Exchange

Most synthetic routes to high-quality nanocrystals with tunable morphologies predominantly employ long hydro-carbon molecules as ligands, which are detrimental for electronic and catalytic applications. Here, a rule is found that the adsorption energy of an organic ligand is related to its carbon-chain length. Using the density functional theory method, the adsorption energies of some commonly used ligand molecules with different carbon-chain lengths are calculated, including carboxylate, hydroxyl, and amine molecules adsorbed on metal or metal oxide crystal surface. The results indicate that the adsorption energy of the ligand molecule with a long carbon chain is weaker than that of a smaller molecule with same functional group. This rule provides a theoretical support for a new kind of ligand exchange method in which large organic ligand molecules can be exchanged by small molecules with same functional group to improve the catalytic properties

Organics- and Surfactant-Free Molten Salt Medium Controlled Synthesis of Pt‑M (M = Cu and Pd) Bi- and Trimetallic Nanocubes and Nanosheets

We present a novel synthetic strategy for the shape-controlled synthesis of Pt-based alloy nanoparticles (NPs) in inorganic molten salt without using any organic surfactants or capping agents. Graphene oxide (GO) was chosen as the stabilizer in the inorganic molten salt synthetic strategy, due to the existence of various oxygen-containing functional groups on its surface, which adsorb, anchor, and stabilize the metal ions or NPs. After GO was added in molten salt, the PtPd nanosheets were formed on its surface in H₂ atmosphere. In addition, when KI was chosen as the shape-inducing agent to selectively adsorb on and fully protect the (100) facets of alloys, PtPd nanocubes with core–shell structure, PtCu nanohemicubes, and PtPdCu nanocubes were prepared successfully on the surface of GO in molten salt. Introduction of GO as the stabilizer in molten salt proves a new approach in synthesis of Pt-based nanocrystals with controlled morphologies

Improving Surface Adsorption via Shape Control of Hematite α‑Fe₂O₃ Nanoparticles for Sensitive Dopamine Sensors

α-Fe₂O₃ nanoparticles (NPs) with morphologies varying from shuttle to drum were synthesized through an anion-assisted and surfactant-free hydrothermal method by simply varying the ratios of ethanol and water in solvent. Control experiments show that the structural evolution can be attributed to a small-molecular-induced anisotropic growth mechanism in which the growth rate of α-Fe₂O₃ NPs along the <i>a</i>-, <i>b</i>-, or <i>c</i>-axis was well-controlled. The detailed structural analysis through the high-resolution transmission electron microscope (HRTEM) indicated that shuttle-like Fe₂O₃ NP surface was covered by high-density atomic steps, which endowed them with the enhanced adsorption and sensor ability toward dopamine (DA). The XPS characterizations indicated that the percentages of the O_C component follow the order of shuttle-like Fe₂O₃ (S-Fe₂O₃ for short) > pseudoshuttle-like Fe₂O₃ (Ps-Fe₂O₃ for short) > polyhedron-like Fe₂O₃ (Ph-Fe₂O₃ for short) > drum-like Fe₂O₃ (D-Fe₂O₃ for short). Benefits from these structural advantages, the S-Fe₂O₃ NPs–Nafion composite electrode exhibited remarkable electrochemical detection ability with a wide liner range from 0.2 μM to 0.107 mM and a low detection limit of 31.25 nM toward DA in the presence of interferents

Synergistic Effect Induced High Photothermal Performance of Au Nanorod@Cu₇S₄ Yolk–Shell Nanooctahedron Particles

Au nanorod (NR) which has strong LSPR (longitudinal surface plasmon resonance) effect in near-infrared (NIR) region was introduced into the Cu₇S₄ hollow NPs to form Au NR@Cu₇S₄ yolk–shell structured nanoparticles (YSNPs) for improving the photothermal property of NPs. The optimum photothermal conversion efficiency of the as-prepared YSNPs is 68.6%. The hybrid YSNPs had the highest photothermal property compared with the equivalent used Au NR and pure Cu₇S₄ because of the synergistic effect of metal and semiconductor. In this case, the synergistic effect in YSNPs was discussed by tuning sizes of the YSNPs and the thickness of Cu₇S₄ shell. The experimental results demonstrated that the NIR photoabsorption and the photothermal conversion performance of Au NR@Cu₇S₄ YSNPs were much dependent on the geometric change of YSNPs, since the electrical field interaction between inner Au NR core and outer Cu₇S₄ shell is closely effected by the distance of two materials and thickness of out-shell, as confirmed by the 3D finite-difference time domain simulation (FDTD) theory simulation. Moreover, we proved that the hollow yolk–shell structure of the YSNPs also endowed the NPs with a large potential in drug delivery

Facile Water-Assisted Synthesis of Cupric Oxide Nanourchins and Their Application as Nonenzymatic Glucose Biosensor

We have demonstrated an interesting approach for the one-pot synthesis of cupric oxide (CuO) nanourchins with sub-100 nm through a sequential dissolution–precipitation process in a water/ethanol system. The first stage produces a precursory crystal [Cu₇Cl₄(OH)₁₀H₂O] that is transformed into monoclinic CuO nanourchins during the following stage. Water is a required reactant for the morphology-controlled growth of different CuO nanostructures. When evaluated for their nonenzymatic glucose-sensing properties, these CuO nanourchins manifest higher sensitivity. Significantly, this water-dependent precursor transformation method may be widely used to effectively control the growth of other metal oxide nanostructures

Sodium Chloride Template Synthesis of Cubic Tin Dioxide Hollow Particles for Lithium Ion Battery Applications

This paper describes a new synthesis and lithium ion charge–discharge property of tin dioxide (SnO₂) hollow nanocubes. SnO₂ is one of the best-known anode materials for lithium-ion battery application because of its high lithiation-delithiation capacity. Hollow nanostructures with high surface area are preferred, because they accommodate large volume changes and maintain the structural stability of electrode materials during charge–discharge cycles. The SnO₂ hollow cubes made in this study had a discharge capacity of up to 1783 mA h g^–1 for the initial cycle and 546 mA h g^–1 after 30 cycles at a current density of 0.2 C between 0.02 and 2.0 V (vs Li/Li⁺)

Structural and Electronic Stabilization of PtNi Concave Octahedral Nanoparticles by P Doping for Oxygen Reduction Reaction in Alkaline Electrolytes

The enhancement in the catalytic activity of PtM (transition metals, TMs) alloy nanoparticles (NPs) results from the electronic structure of Pt being modified by the TM. However, the oxidation of the TM would lead to the electronegativity difference between Pt and TM being much lowered, which induces a decrease in the number of electrons transferred from the TM to Pt, resulting in excessive oxygenated species accumulating on the surface of Pt, thus deteriorating their performance. In this work, the oxygen reduction reaction (ORR) performance of PtNi (Pt₆₈Ni₃₂) concave octahedral NPs (CONPs) in alkaline electrolytes is much improved by doping small amounts of phosphorus. The P-doped PtNi CONPs (P-PtNi) show about 2 and 10 times enhancement for ORR compared to PtNi and commercial Pt/C catalysts. The high-angle annular dark-field scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy mapping characterizations reveal that the P dopant uniformly distributes throughout the CONPs, Pt mainly locates at the edges and corners, whereas Ni situates at the center, forming a P-doped Pt-frame@Ni quasi-core–shell CONP. The X-ray photoelectron spectroscopy spectra indicate that the P dopant obviously increases the electron density of Pt compared with that of PtNi NPs, which contributes to the stabilization of the electronic structure of PtNi CONPs, thus restraining the excessive HO₂^– species produced on the catalysts, which endow them with a high catalytic performance in the ORR. In addition, the P attached to the Ni sites in the PtNi NPs partially prevents the Ni atoms being oxidized by the external O species, which is conducive to the structural and electrochemical stability of the PtNi NPs during the ORR. The present results provide a new insight into the development of ORR catalysts with low utilization of Pt